Why was the stallion so wild

I'm not sure this is chapter 3. I think the Black Stallion is just spirited and independent. As they are preparing to leave port in Arabia, Alec sees four men attempting to lead a wild black stallion up the gangplank onto the ship. Eventually, after a long struggle, they manage to wrestle him into a stall but the stallion hates being contained and every night the passengers can hear him kicking and trying to escape.